The overall objective of this project is to define the nature and role of cellular cytotoxicity phenomena in alloimmune models. Specifically, we wish to define the role of allosensitized T cells, B cells, K cells and macrophages in the in vitro 51Cr-release reaction using normal allo-antigen bearing target cells, and to determine, by direct assessment of cellular activity in rejecting tissue, the in vivo relevance of the in vitro tests. We have been concerned also with control mechanisms involved in the cytotoxic reaction, particularly with regard to the modulating effects of cAMP and cGMP. Further, we are becoming increasingly involved in modulation of lymphocyte proliferation in vitro, and with in vivo administration of agents which can affect both lymphoid proliferation and effector function via the cyclic nucleotide pathway. Specifically, we are working: 1) to refine methods for recovery of infiltrating mononuclear cells from rejecting rat and human allografts, and to verify previous results on cell membrane characteristics by improved techniques for B and T cell identification; 2) to complete a series of comparative experiments on T cell and K cell target killing, using a variety of cyclic nucleotide activating agents and a number of metabolic inhibitors, and to define the precise identity of the insulin-sensitive cell on the in vitro killer assay; 3) to employ the rat MLC as a proliferative model for study of cyclic nucleotide and other control mechanisms; and 4) to establish the value of in vitro cell-mediated killer assays to human renal transplant results.